Isosceles Triangles


In this lesson students explore and use the properties of isosceles triangles to solve real world problems. After learning the basics of isosceles triangles they apply what they learn to the structure of the Eiffel Tower.

A video introduces the topic of isosceles triangles, along with two isosceles triangle theorems. Students are shown how to find the values for the isosceles pair, given the third angle, by solving a multi-step equation.

Students then apply what they have learned about isosceles triangles by learning about the triangular trusses in the Eiffel Tower. Students learn about what a truss is, what their function is in a building, and why isosceles triangle trusses are an effective form of a truss. Students then learn about two important properties of isosceles triangles involve the perpendicular bisector of the base and the angle bisector of the third angle. Another video ties together triangular trusses, perpendicular bisectors, and angle bisectors.

Students then complete a cloze assessment, in which they identify key words that are missing from a reading passage. 

This module can be used as an introductory lesson on isosceles triangles in a middle school geometry unit. The content aligns with grade 7 Core State Standards, but this module can be used as a refresher for higher grades.

This module can be assigned to individual students or groups of students. Students should be able to complete this lesson in 20 minutes.

Math Concepts

  • Triangles
  • Equations

Learning Objectives

  • Define what an isosceles triangle is
  • Describe the isosceles triangle theorems
  • Solve real world problems using isosceles triangles

Prerequisite Skills

  • Basic knowledge of triangles
  • Solving multi-step equations
Common Core Standards CCSS.MATH.CONTENT.7.G.B.5
Lesson Duration 20 mins
Grade Range 6th - 7th Grade

Lesson Preview